I have found that IE9 doesnt seem to like OPC231, and also found that Chrome wont save address details. I have come up with a fix by combining the onepagecheckoutjsfix text file that was supplied with v10.3.
Remember BACKUP before using this file. If anyone with more experience can improve on this file, feel free to do so.
Not a complete package, only checkout.js, overwrite original file found in includes/checkout/

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